1. Field of the Invention
The present invention relates to a trimming circuit that supplies a trimmed voltage according to an external voltage supplied.
2. Description of the Related Art
Since many years ago, a trimmed voltage generated by a trimming circuit has been used to drive semiconductor devices without using an externally supplied power supply voltage as it is, thereby preventing decrease in withstand voltage of transistors and reducing noise and power consumption.
However, with conventional trimming circuits provided in semiconductor devices, the trimmed voltage that is supplied to memory varies due to production variations in the manufacturing process, and hence there is the problem that the trimmed voltage differs for each semiconductor device.
In Japanese Patent Application Laid-Open Publication Kokai No. H03-172906 (hereinafter, also referred to as Patent document 1), an example of a trimming circuit that can solve the above problem is disclosed.
In the Patent document 1, a trimming circuit is disclosed which comprises a series resistor circuit comprising trimming resistors serially connected between the output of a differential amplifier and ground potential, ON/OFF switches connected between the connection points of those resistors and one input terminal of the differential amplifier, a fuse ROM for determining an ON/OFF switch to be driven, and a decoder for supplying a drive signal to the ON/OFF switch based on input signals from the fuse ROM.
The trimming circuit described in the Patent document 1 drives one of the ON/OFF switches ON with use of the drive signal generated based on signals from the fuse ROM, thereby changing a feedback ratio of the series resistor circuit, and thus the trimmed voltage can be set at a desired voltage value.
However, because the series resistor circuit and the differential amplifier have line resistance and line or gate capacitance added thereto, these capacitances need to be charged in a time from the drive start of the ON/OFF switch. The time for the charging causes the problem that the generation or setup of a comparison voltage that is inputted to the one input terminal of the differential amplifier via the series resistor circuit and the ON/OFF switch is delayed.
To solve the above problem, when the resistance of the series resistor circuit is reduced so as to speed up the charging to prevent the generation delay of the comparison voltage, the problem will occur that the steady-state current flowing through the series resistor circuit increases resulting in an increase in consumption current.